U.S. patent application number 15/029961 was filed with the patent office on 2016-10-27 for electroconductive carbon, electrode material containing said carbon, electrode using said electrode material, and power storage device provided with said electrode.
This patent application is currently assigned to NIPPON CHEMI-CON CORPORATION. The applicant listed for this patent is NIPPON CHEMI-CON CORPORATION. Invention is credited to Shuichi ISHIMOTO, Satoshi KUBOTA, Yoshihiro MINATO, Katsuhiko NAOI, Wako NAOI, Kenji TAMAMITSU.
Application Number | 20160315322 15/029961 |
Document ID | / |
Family ID | 52828201 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160315322 |
Kind Code |
A1 |
KUBOTA; Satoshi ; et
al. |
October 27, 2016 |
ELECTROCONDUCTIVE CARBON, ELECTRODE MATERIAL CONTAINING SAID
CARBON, ELECTRODE USING SAID ELECTRODE MATERIAL, AND POWER STORAGE
DEVICE PROVIDED WITH SAID ELECTRODE
Abstract
Provided is conductive carbon which gives an electric storage
device having a high energy density. This conductive carbon is
characterized in having a hydrophilic solid phase component, where
the ratio of the peak area of an amorphous component band in the
vicinity of 1510 cm.sup.-1 against the peak area in a range from
980 to 1780 cm.sup.-1 in a Raman spectrum of the hydrophilic solid
phase component is within a range of 13 to 19%. When performing a
rolling treatment on an active layer including an active particle
and this conductive carbon formed on a current collector during
manufacture of an electrode of an electric storage device, the
pressure resulting from the rolling treatment causes this
conductive carbon to spread in a paste-like form and increase in
density while covering the surface of the active particles, the
conductive carbon being pressed into gaps formed between adjacent
active particles and filling the gaps. As a result, the amount of
active material per unit volume in the electrode obtained after the
rolling treatment increases, and the electrode density
increases.
Inventors: |
KUBOTA; Satoshi; (Tokyo,
JP) ; MINATO; Yoshihiro; (Tokyo, JP) ;
ISHIMOTO; Shuichi; (Tokyo, JP) ; TAMAMITSU;
Kenji; (Tokyo, JP) ; NAOI; Katsuhiko; (Tokyo,
JP) ; NAOI; Wako; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON CHEMI-CON CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON CHEMI-CON
CORPORATION
Tokyo
JP
|
Family ID: |
52828201 |
Appl. No.: |
15/029961 |
Filed: |
October 16, 2014 |
PCT Filed: |
October 16, 2014 |
PCT NO: |
PCT/JP2014/077615 |
371 Date: |
July 6, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/32 20130101;
H01M 10/052 20130101; Y02T 10/70 20130101; H01G 11/42 20130101;
Y02E 60/10 20130101; H01M 4/625 20130101; H01G 11/38 20130101; H01M
4/0435 20130101; C01P 2006/16 20130101; H01G 11/34 20130101; Y02E
60/13 20130101; C01P 2006/40 20130101; C01P 2006/19 20130101; C09C
1/48 20130101; C01B 32/05 20170801; C01B 25/45 20130101 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 4/58 20060101 H01M004/58; H01M 4/525 20060101
H01M004/525; H01G 11/38 20060101 H01G011/38; H01M 4/04 20060101
H01M004/04; H01M 10/0525 20060101 H01M010/0525; H01G 11/42 20060101
H01G011/42; C09C 1/48 20060101 C09C001/48; H01M 4/505 20060101
H01M004/505 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2013 |
JP |
2013-216731 |
Claims
1-10. (canceled)
11. Conductive carbon for an electrode of an electric storage
device, comprising a hydrophilic solid phase component, where a
ratio of a peak area of an amorphous component band in the vicinity
of 1510 cm.sup.-1 against a peak area in a range from 980 to 1780
cm.sup.-1 in a Raman spectrum of the hydrophilic solid phase
component is within a range of 13 to 19%.
12. The conductive carbon according to claim 11, wherein dibutyl
phthalate oil absorption quantity per 100 g of the conductive
carbon is within a range of 100 to 200 mL.
13. The conductive carbon according to claim 11, manufactured by
giving an oxidizing treatment to a carbon raw material having an
inner vacancy.
14. The conductive carbon according to claim 12, manufactured by
giving an oxidizing treatment to a carbon raw material having an
inner vacancy.
15. The conductive carbon according to claim 13, wherein the number
of micropores with a radius of 1.2 nm in the conductive carbon is
0.4 to 0.6 times the number of micropores with a radius of 1.2 nm
in the carbon raw material.
16. The conductive carbon according to claim 14, wherein the number
of micropores with a radius of 1.2 nm in the conductive carbon is
0.4 to 0.6 times the number of micropores with a radius of 1.2 nm
in the carbon raw material.
17. An electrode material for an electric storage device
comprising: the conductive carbon according to claim 11; and an
electrode active material particle.
18. The electrode material according to claim 17, wherein an
average diameter of the electrode active material particles is
within a range of 0.01 to 2 .mu.m.
19. The electrode material according to claim 17, wherein the
electrode active material particles are composed of fine particles
with an average diameter of 0.01 to 2 .mu.m that are operable as a
positive electrode active material or a negative electrode active
material and gross particles with an average diameter of more than
2 .mu.m and not more than 25 .mu.m that are operable as an active
material of the same electrode as the fine particles.
20. The electrode material according to claim 17, further
comprising other conductive carbon.
21. An electrode material for an electric storage device
comprising: the conductive carbon according to claim 12; and an
electrode active material particle.
22. The electrode material according to claim 21, wherein an
average diameter of the electrode active material particles is
within a range of 0.01 to 2 .mu.m.
23. The electrode material according to claim 21, wherein the
electrode active material particles are composed of fine particles
with an average diameter of 0.01 to 2 .mu.m that are operable as a
positive electrode active material or a negative electrode active
material and gross particles with an average diameter of more than
2 .mu.m and not more than 25 .mu.m that are operable as an active
material of the same electrode as the fine particles.
24. The electrode material according to claim 21, further
comprising other conductive carbon.
25. An electrode for an electric storage device, comprising an
active material layer formed by adding pressure to the electrode
material according to claim 17.
26. An electrode for an electric storage device, comprising an
active material layer formed by adding pressure to the electrode
material according to claim 19.
27. An electrode for an electric storage device, comprising an
active material layer formed by adding pressure to the electrode
material according to claim 21.
28. An electrode for an electric storage device, comprising an
active material layer formed by adding pressure to the electrode
material according to claim 23.
29. An electric storage device equipped with the electrode
according to claim 25.
30. An electric storage device equipped with the electrode
according to claim 26.
Description
TECHNICAL FIELD
[0001] The present invention relates to conductive carbon that
gives an electric storage device with a high energy density. The
present invention also relates to an electrode material comprising
the conductive carbon, an electrode using this electrode material,
and an electric storage device equipped with this electrode.
THE RELATED ART
[0002] An electric storage device such as a secondary battery, an
electric double layer capacitor, a redox capacitor and a hybrid
capacitor is a device that is under consideration for wider
application as a battery for an information device including a
cellphone and a notebook-sized personal computer, for a motor drive
power supply of a low-emission vehicle such as an electric vehicle
and a hybrid vehicle, and for an energy recovery system, etc. In
these devices, improvement in energy density is desired to meet the
requirements of higher performance and downsizing.
[0003] In these electric storage devices, an electrode active
material that realizes its capacity by a faradaic reaction
involving the transfer of an electron with an ion in an electrolyte
(including an electrolytic solution) or by a nonfaradaic reaction
not involving the transfer of an electron is used for energy
storage. Further, this active material is generally used in the
form of a composite material with an electroconductive agent. As
the electroconductive agent, conductive carbon such as carbon
black, natural graphite, artificial graphite, and carbon nanotube
is generally used. This conductive carbon, used concurrently with a
low conductive active material, serves to add conductivity to a
composite material, and furthermore, acts as a matrix to absorb the
volume change in accordance with the reaction of the active
material. Also, it serves to ensure an electron conducting path
when the active material is mechanically damaged.
[0004] The composite material of the active material and the
conductive carbon is generally manufactured by a method of mixing
the particles of the active material and the conductive carbon. The
conductive carbon does not make a significant contribution to the
improvement of the energy density of an electric storage device, so
the quantity of the conductive carbon per unit volume needs to be
decreased and that of the active material needs to be increased to
obtain an electric storage device with a high energy density.
Therefore, consideration is given to a method to decrease the
distance between the particles of the active material to increase
the quantity of the active material per unit volume by improving
the dispersibility of the conductive carbon or by reducing the
structure of the conductive carbon. Also, consideration is given to
a method to mix two or more different powder with different
particle diameters as the particles of the active material.
[0005] For example, Patent Document 1 (JP 2004-134304 A) discloses
a nonaqueous secondary battery that is equipped with a positive
electrode that contains a small-sized carbon material having an
average primary particle diameter of 10 to 100 nm (in its example,
acetylene black) and that has a degree of blackness of 1.20 or
more. A coating material used to form the positive electrode is
obtained either by dispersing a mixture of an active material for a
positive electrode, the abovementioned carbon material, a binder
and a solvent by a high shear dispersing machine such as a high
speed rotational homogenizer dispersing machine or a planetary
mixer with three or more rotary axes, or by adding a dispersion
body, in which a mixture of the abovementioned carbon material, a
binder and a solvent are dispersed by a high shear dispersing
machine, into a paste in which a mixture of the active material for
a positive electrode, a binder and a solvent are dispersed, and
further dispersing. By using the device that has a high shearing
force, the carbon material, which is hard to disperse because of
its small particle size, becomes evenly dispersed.
[0006] Also, Patent Document 2 (JP 2009-35598 A) discloses an
electroconductive agent for an electrode for a nonaqueous secondary
battery that consists of acetylene black whose BET-specific surface
area is 30 to 90 m.sup.2/g, dibutylphthalate (DBP) oil absorption
quantity is 50 to 120 mL/100 g, and pH is 9 or more. The electrode
for the secondary battery is formed by dispersing a mixture of this
acetylene black and an active material in a fluid containing a
binder to prepare slurry, and applying this slurry on a current
collector and drying it. Since the acetylene black with the
abovementioned characteristics has a smaller structure compared
with Ketjen Black or other conventional acetylene blacks, the bulk
density of a mixture of the acetylene black and the active material
is improved and the battery capacity is improved.
[0007] Patent Document 3 (JP 6-290780 A) shows that if particles
with a single average diameter are made spherical, their closest
packed structure is either cubic close-packed or hexagonal
close-packed and the packing rate is approximately 0.75, and the
particles cannot be packed further and gaps are formed, and further
shows that the packing rate can be increased by mixing particles
that have so small a diameter that they can fill the gaps between
the particles with a larger diameter. In its working example, an
electrode material, which is prepared by mixing LiCoO.sub.2 having
an average diameter of 10 .mu.m (a particle with a large diameter)
with a particle having a small diameter with the particle diameter
ratio of 0.05 at the mass ratio of 0.2 against the particle with a
large diameter and by mixing the mixture with graphite powder as an
electroconductive agent, is used.
PRIOR ARTS DOCUMENTS
Patent Documents
[0008] Patent Document 1: JP 2004-134304 A
[0009] Patent Document 2: JP 2009-35598 A
[0010] Patent Document 3: JP 6-290780 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0011] Further improvement of an electric storage device in terms
of energy density is always desired. However, the inventors have
examined the prior arts and found that even by the methods
disclosed in Patent Documents 1 and 2, it is difficult to enable
conductive carbon to infiltrate efficiently between the particles
of an active material, and even by the method disclosed in Patent
Document 3, it is difficult to enable a particle with a small
diameter to infiltrate efficiently between larger particles, and
therefore, it is difficult to shorten the distance between active
material particles and increase the amount of the active material
per unit volume. Therefore, the inventors have found that there is
a limitation to the improvement of the energy density with a
positive electrode and/or a negative electrode using the composite
material of particles of an active material and conductive
carbon.
[0012] Therefore, the objective of the present invention is to
provide conductive carbon that steadily gives an electric storage
device with a high energy density.
Means for Solving Problems
[0013] After a keen examination, the inventors have found that
electrode density significantly increases by forming an electrode
of an electric storage device by using a composite material of
conductive carbon, which is obtained by giving a strong oxidizing
treatment to a raw material of conductive carbon with an inner
vacancy, and particles of an active material. Moreover, extensive
analysis of the conductive carbon used revealed that a hydrophilic
solid phase component contained in the conductive carbon has a
large amount of amorphous component that is formed by strong
oxidation of a conjugated double bond of conductive carbon and in
which carbon is bonded by a single bond, and that this component
steadily gives high electrode density.
[0014] Therefore, the present invention, first of all, relates to
conductive carbon for an electrode for an electric storage device,
comprising a hydrophilic solid phase component, where a ratio of a
peak area of an amorphous component band in the vicinity of 1510
cm.sup.-1 against a peak area in the range from 980 to 1780
cm.sup.-1 in a Raman spectrum of the hydrophilic solid phase
component is within a range of 13 to 19%, and preferably 14 to
18%.
[0015] In the present invention, the "hydrophilic solid phase
component" of the conductive carbon refers to the component
collected by the following method: the conductive carbon with
1/1000 of the mass of pure water is added to 20 to 100 mL of pure
water, the conductive carbon is sufficiently dispersed in the pure
water by ultrasonic irradiation for 10 to 60 minutes, this
dispersion is left for 10 to 60 minutes, and a supernatant liquid
is collected. The component taken by the centrifugation as a solid
object from the supernatant liquid is the "hydrophilic solid phase
component." Also, the band in the vicinity of 1510 cm.sup.-1 in a
Raman spectrum is referred to as an amorphous component band
because it is a peak that derives from a carbon single bond
(SP.sup.3 hybridization) formed by strong oxidation of a conjugated
double bond (SP.sup.2 hybridization) of conductive carbon. In the
present invention, the peak area of the amorphous component band in
the hydrophilic solid phase component refers to values calculated
by the following method: for a Raman spectrum in the range from 980
to 1780 cm.sup.-1 obtained by using a laser Raman spectrophotometer
(excitation light: argon ion laser, wavelength 514.5 nm), waveform
separation is conducted by applying the least square method with
regard to the five components:
[0016] Component a: peak in the vicinity of 1180 cm.sup.-1
[0017] Component b: peak in the vicinity of 1350 cm.sup.-1, D
band
[0018] Component c: peak in the vicinity of 1510 cm.sup.-1
[0019] Component d: peak in the vicinity of 1590 cm.sup.-1, G
band
[0020] Component e: peak in the vicinity of 1610 cm.sup.-1
with a fitting analysis program of analysis software (spectra
manager), using the waveforms of mixed Gaussian/Lorentzian
functions, and varying the wave number and half width of each
component, so that they are within the range of the following:
[0021] Component a: wave number 1127-1208 cm.sup.-1, half width
144-311 cm.sup.-1
[0022] Component b: wave number 1343-1358 cm.sup.-1, half width
101-227 cm.sup.-1
[0023] Component c: wave number 1489-1545 cm.sup.-1, half width
110-206 cm.sup.-1
[0024] Component d: wave number 1571-1598 cm.sup.-1, half width
46-101 cm.sup.-1
[0025] Component e: wave number 1599-1624 cm.sup.-1, half width
31-72 cm.sup.-1.
[0026] The following shows the components a to e, the origins
thereof and their bonding state of carbon. The peak area of the
component c, which is obtained as a result of the abovementioned
waveform separation, is the peak area of the amorphous component
band. The peak area in the range from 980 to 1780 cm.sup.-1
corresponds to the total peak areas of the components a to e. The
ratio of the peak area of the amorphous component band in the
vicinity of 1510 cm.sup.-1 against the peak area in the range from
980 to 1780 cm.sup.-1 in a Raman spectrum of the hydrophilic solid
phase component is hereinafter referred to as an "amorphous
component ratio."
TABLE-US-00001 Raman Band: Origin Bonding State of Carbon Component
a: polyene (in the vicinity of 1180 cm.sup.-1) ##STR00001##
Component b: irregular graphite with oxidized edge (in the vicinity
of 1350 cm.sup.-1) ##STR00002## Component c: amorphous component
(in the vicinity of 1510 cm.sup.-1) ##STR00003## Component d: ideal
graphite (in the vicinity of 1590 cm.sup.-1) ##STR00004## Component
e: irregular graphite with oxidized surface (in the vicinity of
1610 cm.sup.-1) ##STR00005##
[0027] In the course of giving a strong oxidizing treatment to a
carbon raw material, the conjugated double bond of conductive
carbon is strongly oxidized and a carbon single bond is formed, and
the amorphous component ratio in the hydrophilic solid phase
component is increased. The conductive carbon of the present
invention, compared with conductive carbon such as Ketjen Black and
acetylene black that are conventionally used to form an electrode
of an electric storage device, has a higher amorphous component
ratio in the hydrophilic solid phase component. If the amorphous
component ratio in the hydrophilic solid phase component of
conductive carbon is increased, the flexibility of conductive
carbon is increased, and if pressure is applied to the conductive
carbon, the particles of the carbon will be transformed and spread
in a paste-like manner. Therefore, if an electrode material is
obtained by mixing particles of an active material for a positive
electrode or an active material for a negative electrode and the
conductive carbon having the hydrophilic solid phase component with
an increased amorphous component ratio, the conductive carbon will
cover the surface of the particles of the active material in the
process of mixing and the dispersibility of the particles of the
active material will be improved. Then, by adding the electrode
material obtained to a solvent in which a binder is solved as
needed, kneading the mixture sufficiently, and applying the kneaded
material obtained onto a current collector to form a positive
electrode or a negative electrode of the electric storage device,
an active material layer is formed, and after this active material
layer is dried as needed, a rolling treatment is given to this
active material layer, and then the conductive carbon spreads in a
paste-like manner due to the applied pressure and becomes dense
while covering the surface of the particle of the active material,
the particles of the active material approach each other, and
accordingly, the conductive carbon is pushed into the gap formed
between the adjacent particles of the active material and fills the
gap densely while covering the surface of the particles of the
active material. As a result, the quantity of an active material
per unit volume of a positive electrode or a negative electrode
that can be obtained after rolling is increased and therefore the
electrode density increases. Also, by using the electrode with this
high electrode density, the energy density of the electric storage
device is increased. If the amorphous component ratio of the
hydrophilic solid phase component is within a range of 13 to 19%,
and preferably 14 to 18%, the electrode density of a positive
electrode or a negative electrode obtained after the rolling
treatment becomes high, and high electrode density can be stably
obtained. If the amorphous component ratio of the hydrophilic solid
phase component is less than 13%, the flexibility of the conductive
carbon decreases, and the electrode density of a positive electrode
or a negative electrode that can be obtained after rolling
decreases. Conductive carbon with a hydrophilic solid phase
component in which the amorphous component ratio is larger than 19%
is hard to manufacture, and the effect of improving the electrode
density tends to be saturated.
[0028] Also, in the course of giving a strong oxidizing treatment
to a carbon raw material, the structure of carbon is severed at the
same time as the amorphous component ratio is increased. The height
of the structure is exhibited by the quantity of DBP oil
absorption, and in a preferable embodiment of the conductive carbon
of the present invention, the quantity of DBP oil absorption per
100 g of the conductive carbon is within the range of 100 to 200
mL. In the present invention, the quantity of DBP oil absorption of
this value is measured in accordance with JIS K 6217-4.
[0029] The conductive carbon of the present invention can be
suitably manufactured by an oxidizing treatment of a carbon raw
material with an inner vacancy. The inner vacancy includes a pore
in porous carbon powder as well as a hollow of Ketjen Black, an
internal or interstitial pore of a carbon nanofiber or a carbon
nanotube. It is difficult to obtain conductive carbon having a
hydrophilic solid phase component that has an amorphous component
ratio within the abovementioned specific ranges by an oxidizing
treatment using a solid carbon raw material. Also, it has been
found that in the course of oxidizing treatment of the carbon raw
material with an inner vacancy, a micropore within the initial
particle of the carbon raw material collapses and disappears due to
fracturing of carbon and a reaction of a surface functional group,
etc. In a preferable embodiment of the conductive carbon of the
present invention, the number of micropores with a radius of 1.2 nm
is decreased to 0.4 to 0.6 times the number of micropores with a
radius of 1.2 nm in the carbon raw material. In the present
invention, the number of micropores with a radius of 1.2 nm can be
obtained from the result of the measurement of a micropore
distribution in accordance with JIS Z8831-2.
[0030] As mentioned above, when a composite material of the
conductive carbon of the present invention and particles of an
electrode active material is employed as an electrode material to
form an electrode of an electric storage device, the energy density
of the electric storage device is improved. Therefore, the present
invention also relates to an electrode material for an electric
storage device comprising the conductive carbon of this invention
and particles of an electrode active material.
[0031] In the electrode material of the present invention, it is
preferable that the average diameter of the particles of the
electrode active material is within a range of 0.01 to 2 .mu.m. A
particle with such a small diameter is likely to aggregate and is
hard to disperse. However, because the flexible conductive carbon
of the present invention attaches to and covers the surface of the
particles of the active material, aggregation of the particles of
the active material can be inhibited even if the average diameter
of the particles of the active material is small. Moreover, it is
preferable that the particles of the electrode active material are
composed of fine particles with an average diameter of 0.01 to 2
.mu.m that are operable as an active material of a positive
electrode or an active material of a negative electrode and gross
particles with an average diameter of more than 2 .mu.m and not
more than 25 .mu.m that are operable as an active material of the
same electrode as the fine particles. The conductive carbon of the
present invention, which has abundant flexibility, attaches to and
covers the surface of the fine particles as well as the surface of
the gross particles, and the aggregation of these particles can be
inhibited and the mixture of the particles of the active material
and the conductive carbon can be homogenized. Further, the gross
particles increase the electrode density and improve the energy
density of an electric storage device. Also, when pressure is
applied to the active material layer that is formed on the current
collector by a rolling treatment in manufacturing the electrode,
the gross particles press the conductive carbon of the present
invention and approach each other, so that the pastification and
densification of the conductive carbon is accelerated. Further, in
the course of the rolling treatment, with the approach of the gross
particles, the fine particles press the conductive carbon of the
present invention and are pushed out into the gaps formed between
adjacent gross particles together with the paste-like conductive
carbon, and fill the gaps densely, so that the electrode density
further increases and the energy density of the electric storage
device further improves. If the average diameter of the fine
particles is 2 .mu.m or less, the electrode density sharply
increases, but if the average diameter of the fine particles is
0.01 .mu.m or less, the effect of improving the electrode density
tends to be saturated. The average diameter of the active material
particles is the 50% diameter (median diameter) as in the
measurement of particle size distribution obtained by using a light
scattering particle size meter.
[0032] In the electrode material of the present invention, it is
preferable that another kind of conductive carbon, especially
conductive carbon that has a higher electroconductivity than the
conductive carbon of the present invention, is further comprised.
When pressure is applied to the electrode material when the
electrode is manufactured, this carbon also densely fills the gaps
formed by the adjacent particles of an active material together
with the conductive carbon of the present invention and the
conductivity of the whole electrode is improved, so that the energy
density of an electric storage device further improves.
[0033] As mentioned above, if an electrode of an electric storage
device is formed with the electrode material comprising the
conductive carbon of the present invention and particles of an
active material, the energy density of the electric storage device
is improved. Therefore, the present invention also relates to an
electrode of an electric storage device that has an active material
layer formed by adding pressure to the electrode material of the
present invention, and an electric storage device that is equipped
with this electrode.
Advantageous Effects of the Invention
[0034] The conductive carbon of the present invention comprising a
hydrophilic solid phase component with an amorphous component ratio
of 13 to 19% has high flexibility, and when pressure is applied to
the conductive carbon, the carbon particle is transformed and
spread in a paste-like manner. In manufacturing the electrode of an
electric storage device, when pressure is applied to the electrode
material in which the particles of an electrode active material and
the conductive carbon of the present invention are mixed, by the
pressure, the conductive carbon of the present invention becomes
spread in a paste-like manner and becomes dense while covering the
surface of the particles of the active material, the particles of
the active material approach each other, and accordingly, the
conductive carbon of the present invention is pushed into the gap
formed between the adjacent particles of the active material and
fills the gap densely. As a result, the quantity of the active
material per unit volume in the electrode is increased and the
electrode density is increased. If the amorphous component ratio in
the hydrophilic solid phase component is 13 to 19%, an electrode
with high electrode density can be stably obtained. Moreover, by
using this electrode with a high electrode density, the energy
density of the electric storage device is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows a graph in which micropore distributions of
conductive carbon in a working example and a comparative example
are compared.
[0036] FIG. 2 shows a graph in which results of ultrafine hardness
test on conductive carbon in a working example and a comparative
example are compared.
[0037] FIG. 3 shows a graph in which ultraviolet visible spectra in
water-soluble fractions of conductive carbon in a working example
and a comparative example are compared.
[0038] FIG. 4 shows graphs in which Raman spectra of hydrophilic
solid phase components in conductive carbon in a working example
and a comparative example are compared.
[0039] FIG. 5 shows SEM images of conductive carbon in a working
example and a comparative example.
[0040] FIG. 6 shows a graph in which the relationship between the
amorphous component ratio and the electrode density is shown.
[0041] FIG. 7 shows a graph in which the relationship between the
average particle diameter of LiCoO.sub.2 fine particles and the
electrode density is shown.
[0042] FIG. 8 shows a graph in which the relationship between the
average particle diameter of
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 fine particles and the
electrode density is shown.
DETAILED DESCRIPTION OF THE INVENTION
[0043] Conductive carbon of the present invention has high
flexibility, and if pressure is applied to the conductive carbon, a
carbon particle is transformed and spread in a paste-like manner.
This characteristic mainly derives from a hydrophilic solid phase
component comprised in the conductive carbon. The conductive carbon
of the present invention has a hydrophilic solid phase component in
which an amorphous component ratio calculated from a Raman spectrum
is within the range of 13 to 19%, and preferably 14 to 18%. If the
amorphous component ratio in the hydrophilic solid phase component
is within the abovementioned range, the electrode density of a
positive electrode or a negative electrode obtained after a rolling
treatment becomes high, and high electrode density can be stably
obtained. If the amorphous component ratio in the hydrophilic solid
phase component is less than 13%, the flexibility of the conductive
carbon decreases, and the electrode density of a positive electrode
or a negative electrode that is obtained after rolling decreases.
Conductive carbon that has a hydrophilic solid phase component in
which the amorphous component ratio is more than 19% is hard to
manufacture, and the effect of improving the electrode density
tends to be saturated.
[0044] The conductive carbon of the present invention is obtained
by giving a strong oxidizing treatment to a carbon raw material,
especially a carbon raw material with an inner vacancy such as
porous carbon powder, Ketjen Black, carbon nanofiber and carbon
nanotube. In the course of a strong oxidizing treatment, a
conjugated double bond of the conductive carbon is strongly
oxidized, a carbon single bond is formed, and the amorphous
component ratio in the hydrophilic solid phase component is
increased.
[0045] Also, in the course of giving a strong oxidizing treatment
to a carbon raw material, a crystallite is fractured and
especially, a crystallite in the graphene surface direction is
severed in a twisted area. The extent of the fracturing of a
crystallite can also be calculated from a Raman spectrum of a
hydrophilic solid phase component in the range from 980 to 1780
cm.sup.-1. To calculate the crystallite size in a graphene surface,
with regard to the following two components:
[0046] Component f: peak in the vicinity of 2700 cm.sup.-1, 2D
band
[0047] Component g: peak in the vicinity of 2900 cm.sup.-1, D+G
band,
the values of using the waveforms of mixed Gaussian/Lorentzian
functions, varying the wave number and half width of each component
so that they are within the range of the following ranges:
[0048] Component f: wave number 2680-2730 cm.sup.-1, half width
100-280 cm.sup.-1
[0049] Component g: wave number 2900-2945 cm.sup.-1, half width
100-280 cm.sup.-1,
and conducting waveform separation applying the least square method
are used concurrently. Then, with the peak area of the component d
or the G band, the peak area of the component b or the D band, and
the peak area of the component f or the 2D band, which are obtained
by the waveform separation, a crystallite size La that does not
include a twist in a graphene surface direction and a crystallite
size Leq that includes a twist in a graphene surface direction are
calculated by the following formulae. The calculation of La and Leq
from a Raman spectrum with the following formulae is known (CARBON
48 (2010) 620-629):
La=4.4.times.(the peak area of G band/the peak area of D
band)nm
Leq=8.8.times.(the peak area of 2D band/the peak area of D
band)nm.
[0050] The relationship between La and Leq is shown conceptually in
the following diagrams, where (A) shows a crystallite with a twist
on the graphene surface and (B) shows a crystallite without a twist
on the graphene surface. The more the value of Leq/La deviates from
1, the more crystallites with a twist on the graphene surface
included. Also, it has been found that the value of Leq/La
increases as the value of La increases. In a preferable embodiment
of the conductive carbon of the present invention, La and Leq
satisfy the following relationships:
1.3 nm.ltoreq.La.ltoreq.1.5 nm, and
1.5 nm.ltoreq.Leq.ltoreq.2.3 nm, and
1.0.ltoreq.Leq/La.ltoreq.1.55.
Within these ranges, improvement in electrode density is especially
realized.
##STR00006##
[0051] Also, in the course of giving a strong oxidizing treatment
to a carbon raw material, the structure of carbon is severed at the
same time as the amorphous component ratio of the hydrophilic solid
phase component is increased. In a preferable embodiment of the
conductive carbon of the present invention, the quantity of DBP oil
absorption is within the range of 100 to 200 mL/100 g.
[0052] Also, it has been found that, in the course of oxidizing
treatment of the carbon raw material with an inner vacancy, a
micropore within the initial particle of the carbon raw material
collapses and disappears, and the specific surface area decreases
due to fracturing of carbon and a reaction of a surface functional
group, etc. In a preferable embodiment of the conductive carbon of
the present invention, the number of micropores with a radius of
1.2 nm is decreased to 0.4 to 0.6 times the number of micropores
with a radius of 1.2 nm in the carbon raw material. Also, in a
preferable embodiment of the conductive carbon of the present
invention, the specific surface area is within the range of 650 to
800 cm.sup.2/g. The specific surface area means a value measured in
accordance with JIS Z8830.
[0053] The conductive carbon of the present invention can be
suitably obtained by the first manufacturing method comprising:
(a1) a process in which oxidizing treatment is given to a carbon
raw material with an inner vacancy; (b1) a process in which the
product after oxidizing treatment and a transition metal compound
are mixed; (c1) a process in which the mixture obtained is
pulverized to produce a mechanochemical reaction; (d1) a process in
which the product after the mechanochemical reaction is heated in a
nonoxidizing atmosphere; and (e1) a process in which the
aforementioned transition metal compound and/or its reaction
product is removed from the product after heating.
[0054] In the first manufacturing method, carbon with an inner
vacancy such as porous carbon powder, Ketjen Black, carbon
nanofiber and carbon nanotube is used as the carbon raw material.
As such a carbon raw material, Ketjen Black is preferable. If solid
carbon is used as a raw material and the same treatment as the
first manufacturing method is used, the conductive carbon of the
present invention is difficult to obtain.
[0055] In the (a1) process, the carbon raw material is left
immersed in acid. As acid, an acid usually used for an oxidizing
treatment of carbon such as nitric acid, a mixture of nitric acid
and sulfuric acid, and an aqueous solution of hypochlorous acid can
be used. The immersion time depends on the concentration of acid or
the quantity of the carbon raw material to be treated, and is
usually within the range of 5 minutes to 1 hour. The carbon after
oxidizing treatment is sufficiently washed by water and dried, and
then mixed with a transition metal compound in the (b1)
process.
[0056] For the chemical compound of transition metal to be added to
the carbon raw material in the (b1) process, an inorganic metallic
salt of transition metal such as a halide, nitrate, sulfate and
carbonate; an organic metallic salt of transition metal such as
formate, acetate, oxalate, methoxide, ethoxide and isopropoxide; or
a mixture thereof can be used. These chemical compounds can be used
alone, or two or more kinds can be used as a mixture. Chemical
compounds that contain different transition metals can be mixed in
a prescribed amount and used. Also, a chemical compound other than
the chemical compound of transition metal, such as an alkali metal
compound, can be added concurrently unless it has an adverse effect
on the reaction. Since the conductive carbon of the present
invention is mixed with particles of an electrode active material
and used in manufacturing an electrode of an electric storage
device, it is preferable that a chemical compound of an element
constituting the active material is added to the carbon raw
material so that adulteration of an element that can serve as
impurities against the active material can be prevented.
[0057] In the (c1) process, the mixture obtained in the (b1)
process is pulverized and a mechanochemical reaction is produced.
Examples of a powdering machine for this reaction are a mashing
machine, millstone grinder, ball mill, bead mill, rod mill, roller
mill, agitation mill, planetary mill, vibrating mill, hybridizer,
mechanochemical composite device and jet mill. Milling time depends
on the powdering machine used or the quantity of the carbon to be
treated and has no strict restrictions, but is generally within the
range of 5 minutes to 3 hours. The (d1) process is conducted in a
nonoxidizing atmosphere such as a nitrogen atmosphere and an argon
atmosphere. The temperature and time of heating is chosen in
accordance with the chemical compound of transition metal used. In
the subsequent (e1) process, the conductive carbon of the present
invention can be obtained by removing the chemical compound of
transition metal and/or its reaction product from the product that
has been heated by means of acid dissolution etc., then
sufficiently washing and drying them.
[0058] In the first manufacturing method, the chemical compound of
transition metal promotes the oxidation of the carbon raw material
by mechanochemical reaction in the (c 1) process, and the oxidation
of the carbon raw material rapidly proceeds. By this oxidation, the
structure is severed and simultaneously a conjugated double bond of
the conductive carbon is oxidized and a carbon single bond is
formed, and the flexible conductive carbon with a hydrophilic solid
phase component that has an amorphous component ratio within the
range of 13 to 19% can be obtained.
[0059] The conductive carbon of the present invention can also be
suitably obtained by the second manufacturing method that
comprises:
(a2) a process in which a carbon raw material with an inner vacancy
and a chemical compound of transition metal are mixed; (b2) a
process in which the mixture obtained is heated in an oxidizing
atmosphere; and (c2) a process in which the abovementioned chemical
compound of transition metal and/or its reaction product is removed
from the product after heat treatment.
[0060] In the second manufacturing method, as the carbon raw
material, carbon with an inner vacancy such as porous carbon
powder, Ketjen Black, carbon nanofiber and carbon nanotube is used.
As such a carbon raw material, Ketjen Black is preferable. If solid
carbon is used as a raw material and the same treatment as the
second manufacturing method is used, it is difficult to obtain the
conductive carbon of the present invention.
[0061] As the chemical compound of transition metal to be added to
the carbon raw material in the (a2) process, an inorganic metallic
salt of transition metal such as a halide, nitrate, sulfate and
carbonate; an organic metallic salt of transition metal such as
formate, acetate, oxalate, methoxide, ethoxide and isopropoxide; or
a mixture thereof can be used. These chemical compounds can be used
alone, or two or more kinds can be mixed and used. Chemical
compounds that contain different transition metals can be mixed in
a prescribed amount and used. Moreover, a chemical compound other
than a chemical compound of transition metal such as a chemical
compound of alkali metal can be added concurrently unless it has an
adverse effect on the reaction. This conductive carbon is mixed
with the particle of an electrode active material particle and used
in manufacturing an electrode of an electric storage device, so it
is preferable to add a chemical compound of an element that
constitutes the active material to the carbon raw material because
this will prevent the mixing of an element that can be impurities
against the active material.
[0062] The (b2) process is conducted in an oxidizing atmosphere,
for example in air, and at a temperature at which carbon does not
disappear, preferably at a temperature of 200 to 350.degree. C. In
the subsequent (c2) process, the conductive carbon of the present
invention can be obtained by removing the chemical compound of
transition metal and/or its reaction product from the product that
has been heated by means of acid dissolution etc., then
sufficiently washing and drying them.
[0063] In the second manufacturing method, the chemical compound of
transition metal acts as a catalyst to oxidize the carbon raw
material in the heating process in an oxidizing atmosphere and the
oxidation of the carbon raw material rapidly proceeds. By this
oxidization, the structure is severed and simultaneously a
conjugated double bond of the conductive carbon is oxidized and a
carbon single bond is formed, and the flexible conductive carbon
with a hydrophilic solid phase component that has an amorphous
component ratio within the range of 13 to 19% can be obtained.
[0064] The conductive carbon of the present invention can be
obtained by giving a strong oxidizing treatment to a carbon raw
material with an inner vacancy, but it is also possible to promote
the oxidation of the carbon raw material by a method other than the
first manufacturing method or the second manufacturing method.
[0065] The conductive carbon of the present invention is used for
an electrode of an electric storage device such as a secondary
battery, an electric double layer capacitor, a redox capacitor and
a hybrid capacitor in an embodiment in which the conductive carbon
of the present invention is mixed with a particle of an electrode
active material that realizes its capacity by a faradaic reaction
that involves the transfer of an electron between an ion in the
electrolyte of the electric storage device or a nonfaradaic
reaction that does not involve the transfer of an electron. The
electric storage device comprises a pair of electrodes (a positive
electrode and a negative electrode) and an electrolyte that is
placed between the electrodes as essential elements, and at least
one of the positive electrode and the negative electrode is
manufactured with an electrode material comprising the conductive
carbon of the present invention and the particle of an electrode
active material.
[0066] The electrolyte that is placed between a positive electrode
and a negative electrode in an electric storage device can be an
electrolytic solution that is held by a separator, a solid
electrolyte, or a gel electrolyte, that is, an electrolyte that is
used in a conventional electric storage device can be used without
any restrictions. Representative electrolytes are as follows. For a
lithium ion secondary battery, an electrolytic solution in which a
lithium salt such as LiPF.sub.6, LiBF.sub.4, LiCF.sub.3SO.sub.3 and
LiN(CF.sub.3SO.sub.2).sub.2 is dissolved in a solvent such as
ethylene carbonate, propylene carbonate, butylene carbonate and
dimethylcarbonate can be used and held by a separator such as
polyolefin fiber nonwoven fabric and glass fiber nonwoven fabric.
Further, an inorganic solid electrolyte such as
Li.sub.5La.sub.3Nb.sub.2O.sub.12,
Li.sub.1.5Al.sub.0.5Ti.sub.1.5(PO.sub.4).sub.3,
Li.sub.7La.sub.3Zr.sub.2O.sub.12 and Li.sub.7P.sub.3S.sub.11, an
organic solid electrolyte that is composed of a complex of a
lithium salt and a macromolecule compound such as polyethylene
oxide, polymethacrylate and polyacrylate, and a gel electrolyte in
which an electrolytic solution is absorbed into polyvinylidene
fluoride and polyacrylonitrile etc. are also used. For an electric
double layer capacitor and a redox capacitor, an electrolytic
solution in which a quaternary ammonium salt such as
(C.sub.2H.sub.5).sub.4NBF.sub.4 is dissolved in a solvent such as
acrylonitrile and propylene carbonate is used. For a hybrid
capacitor, an electrolytic solution in which a lithium salt is
dissolved in propylene carbonate etc. or an electrolytic solution
in which a quaternary ammonium salt is dissolved into propylene
carbonate etc. is used.
[0067] The positive electrode or negative electrode of an electric
storage device is generally manufactured by sufficiently kneading
an electrode material comprising the conductive carbon of the
present invention and the particles of an electrode active material
together with a solvent in which a binder is dissolved as needed,
forming an active material layer by applying the kneaded material
obtained onto a current collector to form the positive electrode or
negative electrode of the electric storage device by the doctor
blade method etc., drying this active material layer as needed, and
then giving the active material layer a rolling treatment. It is
also suitable to form the kneaded substance obtained into a
prescribed shape, crimp this onto a current collector and then give
a rolling treatment to this. In the case where a solid electrolyte
or a gel electrolyte is used as an electrolyte between a positive
electrode and a negative electrode, a solid electrolyte is added to
an electrode material comprising the conductive carbon of the
present invention and an electrode active material particle in
order to ensure an ion conductive pass in the active material
layer. The mixture obtained is sufficiently kneaded together with a
solvent in which a binder is dissolved as needed, an active
material layer is formed using the kneaded material obtained, and a
rolling treatment is given to this.
[0068] In the process to manufacture the electrode material by
mixing the conductive carbon of the present invention and the
electrode active material particles, the conductive carbon is
attached to the surface of the active material particles and covers
the surface, so that the aggregation of the active material
particles can be inhibited. Also, by applying pressure in the
course of a rolling treatment of the active material layer, a large
area or all of the conductive carbon of the present invention
spreads in a paste-like manner and becomes dense while covering the
surface of the active material particles, the active material
particles approach each other, and as a result, the conductive
carbon of the present invention is pushed into the gap formed
between the adjacent particles of the active material and fills the
gap densely while covering the surface of the particles of the
active material. Therefore, the quantity of the active material per
unit volume in the electrode is increased, and the electrode
density is increased. Also, by using the electrode with an
increased electrode density, the energy density of the electric
storage device is improved. This reveals that the densely filled
paste-like conductive carbon has enough conductivity to serve as an
electroactive agent and does not inhibit the impregnation of the
electrolytic solution in the electric storage device.
[0069] As the active material for a positive electrode and an
active material for a negative electrode that are mixed with the
conductive carbon of the present invention in the manufacture of an
electrode material, an active material for an electrode that is
used in a conventional electric storage device can be used without
any specific restrictions. The active material can be a single
chemical compound or a mixture of two or more kinds of chemical
compound.
[0070] Examples of a positive electrode active material for a
secondary battery are, among all, LiMO.sub.2 having a laminar rock
salt structure, laminar Li.sub.2MnO.sub.3-LiMO.sub.2 solid
solution, and spinel LiM.sub.2O.sub.4 (M in the formula signifies
Mn, Fe, Co, Ni or a combination thereof). Specific examples of
these are LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.4/5Co.sub.1/5O.sub.2,
LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2,
LiNi.sub.1/2Mn.sub.1/2O.sub.2, LiFeO.sub.2, LiMnO.sub.2,
Li.sub.2MnO.sub.3--LiCoO.sub.2, Li.sub.2MnO.sub.3--LiNiO.sub.2,
Li.sub.2MnO.sub.3--LiNi.sub.1/3CO.sub.1/3Mn.sub.1/3O.sub.2,
Li.sub.2MnO.sub.3--LiNi.sub.1/2Mn.sub.1/2O.sub.2,
Li.sub.2MnO.sub.3--LiNi.sub.1/2Mn.sub.1/2O.sub.2--LiNi.sub.1/3Co.sub.1/3M-
n.sub.1/3O.sub.2, LiMn.sub.2O.sub.4 and
LiMn.sub.3/2Ni.sub.1/2O.sub.4. Other examples include sulfur and a
sulfide such as Li.sub.2S, TiS.sub.2, MoS.sub.2, FeS.sub.2,
VS.sub.2 and Cr.sub.1/2V.sub.1/2S.sub.2, a selenide such as
NbSe.sub.3, VSe.sub.2 and NbSe.sub.3, an oxide such as
Cr.sub.2O.sub.5, Cr.sub.3O.sub.8, VO.sub.2, V.sub.3O.sub.8,
V.sub.2O.sub.5 and V.sub.6O.sub.13 as well as a complex oxide such
as LiNi.sub.0.8Co.sub.0.15Al.sub.0.05O.sub.2, LiVOPO.sub.4,
LiV.sub.3O.sub.5, LiV.sub.3O.sub.8, MoV.sub.2O.sub.8,
Li.sub.2FeSiO.sub.4, Li.sub.2MnSiO.sub.4, LiFePO.sub.4,
LiFe.sub.1/2Mn.sub.1/2PO.sub.4, LiMnPO.sub.4 and
Li.sub.3V.sub.2(PO.sub.4).sub.3.
[0071] Examples of a negative electrode active material for a
secondary battery are an oxide such as Fe.sub.2O.sub.3, MnO,
MnO.sub.2, Mn.sub.2O.sub.3, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4,
NiO, Ni.sub.2O.sub.3, TiO, TiO.sub.2, SnO, SnO.sub.2, SiO.sub.2,
RuO.sub.2, WO, WO.sub.2 and ZnO, metal such as Sn, Si, Al and Zn, a
complex oxide such as LiVO.sub.2, Li.sub.3VO.sub.4 and
Li.sub.4Ti.sub.5O.sub.12, and a nitride such as
Li.sub.2.6Co.sub.0.4N, Ge.sub.3N.sub.4, Zn.sub.3N.sub.2 and
Cu.sub.3N.
[0072] As an active material in a polarizable electrode of an
electric double layer capacitor, a carbon material with a large
specific surface area such as activated carbon, carbon nanofiber,
carbon nanotube, phenol resin carbide, polyvinylidene chloride
carbide and microcrystal carbon is exemplified. In a hybrid
capacitor, a positive electrode active material exemplified for a
secondary battery can be used as a positive electrode. In this
case, a negative electrode is composed of a polarizable electrode
using activated carbon etc. Also, a negative electrode active
material exemplified for a secondary battery can be used as a
negative electrode. In this case, a positive electrode is composed
of a polarizable electrode using activated carbon etc. As a
positive electrode active material of a redox capacitor, a metal
oxide such as RuO.sub.2, MnO.sub.2 and NiO is exemplified, and a
negative electrode is composed of an active material such as
RuO.sub.2 and a polarizable material such as activated carbon.
[0073] The shape and particle diameter of active material particles
have no restrictions. Even if active material particles with an
average diameter of 0.01 to 2 .mu.m, which are generally easy to
aggregate and difficult to disperse, is used, the aggregation of
the active material particles can be suitably inhibited because the
conductive carbon of the present invention, which has high
flexibility, is attached to the surface of the active material
particles and covers their surface. Also, it is preferable that the
active material particles are composed of gross particles with a
particle diameter of 1 .mu.m or more and preferably 5 .mu.m or
more, and fine particles with a particle diameter of such a size
that enables the fine particles to go into a gap formed by adjacent
gross particles, preferably a particle diameter of one fifth or
less of the gross particle and especially preferably one tenth or
less of the gross particle, and that are operable as an active
material of the same electrode as the gross particles. Especially,
it is preferable that the active material particles are composed of
fine particles with an average diameter of 0.01 to 2 .mu.m and
gross particles that are operable as an active material of the same
electrode as the fine particles and that has an average diameter of
more than 2 .mu.m and not more than 25 .mu.m. Since the highly
flexible conductive carbon of the present invention is attached to
and covers not only the surface of the gross particles but the
surface of the fine particles in the manufacturing process of the
electrode material, the highly flexible conductive carbon of the
present invention can effectively inhibit the aggregation of these
particles and improve the dispersion of the active material
particles. Moreover, the gross particles increase the electrode
density and improve the energy density of an electric storage
device. Further, by the pressure due to a rolling treatment in
manufacturing an electrode that is added to an active material
layer that is formed on a current collector, the gross particles
approach each other while pressing the conductive carbon of the
present invention, and thus the pastification and densification of
the conductive carbon is promoted. Also, in the course of a rolling
treatment, as the gross particles approach each other, the fine
particles press the conductive carbon of the present invention, are
pushed into the gap formed between the adjacent gross particles
together with the conductive carbon that is spread in a paste-like
manner, and fill the gap densely, and the electrode density further
increases and the energy density of the electric storage device
further improves. If the average diameter of the fine particles is
2 .mu.m or less, the electrode density rapidly increases, and if
the average diameter of the fine particles is 0.01 .mu.m or less,
the effect of improving the electrode density tends to be
saturated.
[0074] Also, the conductive carbon of the present invention can be
used concurrently with conductive carbon other than the conductive
carbon of the present invention, including carbon black such as
Ketjen Black, acetylene black and channel black, fullerene, carbon
nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural
graphite, artificial graphite, graphitization KetjenBlack,
mesoporous carbon, and vapor grown carbon fiber etc., which is used
for an electrode of a conventional electric storage device.
Especially, it is preferable to use concurrently carbon that has a
higher electroconductivity than the electroconductivity of the
conductive carbon of the present invention. Since the conductive
carbon of the present invention is attached to and covers not only
the surface of the active material particles, but also the surface
of the conductive carbon used concurrently, the aggregation of the
conductive carbon used concurrently can be inhibited. Moreover, by
the pressure added to the active material layer formed on the
current collector by a rolling treatment in manufacturing the
electrode, the conductive carbon used concurrently densely fills
the gap formed between the adjacent particles together with the
conductive carbon of the present invention that is spread in a
paste-like manner, and the electroconductivity of the entire
electrode improves, and thus the energy density of the electric
storage device further improves.
[0075] The method to mix the active material particles, the
conductive carbon of the present invention and the other conductive
carbon used concurrently as needed in manufacturing an electrode
material has no restrictions, and a heretofore known method of
mixing can be used. However, it is preferable to mix by dry mixing,
and for dry mixing a mashing machine, millstone grinder, ball mill,
bead mill, rod mill, roller mill, agitation mill, planetary mill,
vibration mill, hybridizer, mechanochemical composite device and
jet mill can be used. Especially, it is preferable to give a
mechanochemical treatment to the active material particles and the
conductive carbon of the present invention because the coatability
and the evenness of the covering of the active material particles
by the conductive carbon of the present invention are improved. The
ratio of the amount of the active material particles and that of
the conductive carbon of the present invention or the total amount
of the conductive carbon of the present invention and the other
conductive carbon used concurrently as needed is preferably within
the range of 90:10 to 99.5:0.5 mass ratio and more preferably
within the range of 95:5 to 99:1 in order to obtain an electric
storage device with a high energy density. If the ratio of the
conductive carbon is lower than the abovementioned range, the
conductivity of the active material layer tends to become
insufficient, and the covering rate of the active material
particles by the conductive carbon tends to decrease. Also, if the
ratio of the conductive carbon is larger than the abovementioned
range, the electrode density tends to decrease and the energy
density of the electric storage device tends to decrease.
[0076] As the current collector for an electrode of an electric
storage device, an electroconductive material such as platinum,
gold, nickel, aluminum, titanium, steel and carbon can be used. For
the form of the current collector, any form such as a film, foil,
plate, net, expanded metal, or cylinder can be adopted.
[0077] As the binder to be mixed with the electrode material, a
heretofore known binder such as polytetrafluoroethylene,
polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene
copolymer, polyvinyl fluoride and carboxymethylcellulose can be
used. It is preferable that the amount of binder used is 1 to 30%
by mass of the total amount of the mixed material. If the amount of
binder used is 1% by mass or less, the strength of the active layer
is not sufficient, and if the amount of binder used is 30% by mass
or more, drawbacks such as a decrease in the discharge capacity of
an electrode or excessive internal resistance arise. As the solvent
to be mixed with the electrode material, a solvent such as N-methyl
pyrrolidone that does not adversely affect the electrode material
can be used without any restriction.
EXAMPLES
[0078] The present invention is explained in the following
examples, though the present invention is not limited to the
following examples.
(1) Conductive Carbon Manufactured by the First Manufacturing
Method and an Electrode Containing the Carbon Obtained
Example 1
[0079] Ketjen Black (trade name: ECP600JP, manufacturer: Ketjen
Black International Co.) weighing 10 g was added to 300 mL of 60%
nitric acid and then the fluid obtained was irradiated by an
ultrasonic wave for 10 minutes, and then the fluid was filtered and
the Ketjen Black was retrieved. The retrieved Ketjen Black was
washed with water three times and then dried, so that oxidized
Ketjen Black was obtained. Then, 0.5 g of the oxidized Ketjen Black
obtained was mixed with 1.98 g Fe(CH.sub.3COO).sub.2, 0.77 g
Li(CH.sub.3COO), 1.10 g C.sub.6H.sub.8O.sub.7.H.sub.2O, 1.32 g
CH.sub.3COOH, 1.31 g H.sub.3PO.sub.4, and 120 mL distilled water,
and the mixed fluid obtained was agitated by a stirrer for 1 hour,
and then the mixed fluid was evaporated, dried and solidified at
100.degree. C. in air and a mixture was collected. Then, the
mixture obtained was introduced into a vibratory ball mill device
and pulverization was conducted at 20 Hz for 10 minutes. The powder
obtained by pulverization was heated at 700.degree. C. for 3
minutes in nitrogen, and a complex in which LiFePO.sub.4 was
supported by Ketjen Black was obtained.
[0080] 1 g of the complex obtained was added to 100 mL of 30%
hydrochloric acid aqueous solution, then the LiFePO.sub.4 in the
complex was dissolved by irradiating the fluid obtained with an
ultrasonic wave for 15 minutes, and the remaining solid matter was
filtered, washed with water and dried. A part of the solid matter
after drying was heated to 900.degree. C. in air and its weight
loss was measured by TG analysis. Until it was confirmed that the
weight loss was 100%, that is, no LiFePO.sub.4 remained, the
abovementioned process of dissolving LiFePO.sub.4 in the
hydrochloric acid aqueous solution, filtering, washing with water
and drying was repeated, so that conductive carbon that did not
contain any LiFePO.sub.4 was obtained.
[0081] Then, the DBP absorption quantity, specific surface area and
micropore distribution of the conductive carbon obtained were
measured. Further, 40 mg of the conductive carbon obtained was
added to 40 mL of pure water, and then the carbon was dispersed in
the pure water by applying ultrasonic irradiation for 30 minutes.
The resultant supernatant solution was collected and centrifuged, a
solid phase area was gathered and dried, and a hydrophilic solid
phase component was obtained. For the hydrophilic solid phase
component obtained, a Raman spectrum was measured with a
microscopic Raman measurement device (excitation ray: argon ion
laser; wavelength: 514.5 nm). From the Raman spectrum obtained, the
amorphous component ratio, as well as the crystalline size La,
which does not include a twist in the graphene surface direction,
and crystalline size Leq, which includes a twist in the graphene
surface direction, and Leq/La were calculated.
[0082] Fe(CH.sub.3COO).sub.2, Li(CH.sub.3COO),
C.sub.6H.sub.8O.sub.7.H.sub.2O, CH.sub.3COOH and H.sub.3PO.sub.4
were introduced into distilled water, and the compound liquid
obtained was agitated by a stirrer for 1 hour, and then the
compound liquid was evaporated, dried and solidified at 100.degree.
C. in air and then heated at 700.degree. C. for 3 minutes in
nitrogen, and LiFePO.sub.4 fine particles with an initial particle
diameter of 100 nm were obtained. Then, commercially available
LiFePO.sub.4 gross particles (initial particle diameter: 0.5 to 1
.mu.m, secondary particle diameter: 2 to 3 .mu.m), the fine
particles obtained and the abovementioned conductive carbon were
mixed at the ratio of 90:9:1, and an electrode material was
obtained. Then, 5% by mass of the total mass of polyvinylidene
fluoride and an adequate quantity of N-methyl pyrrolidone were
added to the electrode material and kneaded sufficiently so that
slurry was formed, and this slurry was coated on an aluminum foil,
and an active material layer was formed. The active material layer
was dried and then given a rolling treatment, and a positive
electrode of a lithium ion secondary battery was obtained. The
electrode density of the positive electrode was calculated from the
measured values of the volume and weight of the active material
layer on the aluminum foil in the positive electrode.
Example 2
[0083] The procedure of Example 1 was repeated except that the
process in which 0.5 g oxidized Ketjen Black, 1.98 g
Fe(CH.sub.3COO).sub.2, 0.77 g Li(CH.sub.3COO), 1.10 g
C.sub.6H.sub.8O.sub.7.H.sub.2O, 1.32 g CH.sub.3COOH, 1.31 g
H.sub.3PO.sub.4 and 120 mL distilled water were mixed was changed
into a process in which 1.8 g oxidized Ketjen Black, 1.98 g
Fe(CH.sub.3COO).sub.2, 0.77 g Li(CH.sub.3COO), 1.10 g
C.sub.6H.sub.8O.sub.7.H.sub.2O, 1.32 g CH.sub.3COOH, 1.31 g
H.sub.3PO.sub.4 and 250 mL distilled water were mixed.
Example 3
[0084] The procedure of Example 1 was repeated except that the
process in which 0.5 g oxidized Ketjen Black, 1.98 g
Fe(CH.sub.3COO).sub.2, 0.77 g Li(CH.sub.3COO), 1.10 g
C.sub.6H.sub.8O.sub.7.H.sub.2O, 1.32 g CH.sub.3COOH, 1.31 g
H.sub.3PO.sub.4 and 120 mL distilled water were mixed was changed
into a process in which 1.8 g oxidized Ketjen Black, 0.5 g
Fe(CH.sub.3COO).sub.2, 0.19 g Li(CH.sub.3COO), 0.28 g
C.sub.6H.sub.8O.sub.7.H.sub.2O, 0.33 g CH.sub.3COOH, 0.33 g
H.sub.3PO.sub.4 and 250 mL distilled water were mixed.
Comparative Example 1
[0085] The oxidized Ketjen Black obtained in Example 1 was
introduced into a vibratory ball mill device and pulverization was
conducted at 20 Hz for 10 minutes. The powder obtained by
pulverization were heated at 700.degree. C. for 3 minutes in
nitrogen. Then, the DBP absorption quantity, specific surface area
and micropore distribution of the conductive carbon obtained were
measured. Further, 40 mg of the conductive carbon obtained was
added to 40 mL of pure water, and the amorphous component ratio,
La, Leq, and Leq/La of the hydrophilic solid phase component were
calculated by the same method as the method in Example 1. Also,
with the conductive carbon obtained, a positive electrode that
contained LiFePO.sub.4 was formed by the same method as the method
in Example 1, and its electrode density was calculated.
Comparative Example 2
[0086] The DBP oil absorption quantity, specific surface area and
micropore distribution of the Ketjen Black raw material used in
Example 1 were measured. Also, 40 mg of the Ketjen Black raw
material used in Example 1 was added to 40 mL pure water, and the
amorphous component ratio, La, Leq, and Leq/La of the hydrophilic
solid phase component were calculated by the same method as the
method in Example 1. Moreover, by using the Ketjen Black raw
material, a positive electrode that contained LiFePO.sub.4 was
formed by the same method as the method in Example 1, and its
electrode density was calculated.
[0087] Table 1 shows the amorphous component ratio, La, Leq and
Leq/La, DBP oil absorption quantity, specific surface area, ratio
of the number of pores with the radius of 1.2 nm in the conductive
carbon manufactured from the carbon raw material against the number
of pores with the radius of 1.2 nm in the carbon raw material,
which was calculated from the result of the measurement of pore
distribution, of the conductive carbon and the value of electrode
density in Examples 1 to 3 and Comparative Examples 1 and 2. It
shows that the electrode density is not increased, that is, the
quantity of active material particles in an electrode material is
not increased, even if the conductive carbon in Comparative
Examples 1 and 2, in which the amorphous component ratio of the
hydrophilic solid phase component is less than 13%, is used.
TABLE-US-00002 TABLE 1 The characteristics of conductive carbon and
electrode densities DBP oil Amorphous absorption Ratio of the
Specific Electrode component Leq La quantity number of pores
surface area density ratio (%) (nm) (nm) Leq/La (mL/100 g) (radius
1.2 nm) (cm.sup.2/g) (g/cc) Example 1 17.5 1.69 1.30 1.3 130 0.45
670 2.75 Example 2 17.3 1.80 1.40 1.3 150 0.55 690 2.72 Example 3
14.3 2.20 1.50 1.5 180 0.59 740 2.65 Comparative 11.9 2.35 1.55 1.6
210 0.66 950 2.50 Example 1 Comparative 9.8 3.10 1.60 1.9 350 1.00
1170 2.30 Example 2
[0088] By comparing the conductive carbon (Ketjen Black raw
material) of Comparative Example 2 and the conductive carbon
obtained in Example 1, the effect of the process of the acid
treatment of a carbon raw material.fwdarw.mixing a metal chemical
compound.fwdarw.pulverization.fwdarw.heating in nitrogen
(hereinafter referred to as a "strong oxidizing process") in
Example 1 can be observed.
[0089] FIG. 1 is a graph that shows the result of the measurement
of micropore distribution concerning the conductive carbon in
Comparative Example 2 and Example 1. As a result of the strong
oxidizing process, pores with a radius of approximately 25 nm or
more that are found in carbon with a developed structure and that
appear in area A almost disappear, and the number of pores with a
radius of approximately 5 nm or less that are found in an initial
particle and that appear in area B is significantly decreased.
Therefore, it was found that the structure was severed and the pore
in the initial particle collapsed by the strong oxidizing process.
Also, the severance of the structure was confirmed by the
abovementioned DBP oil absorption quantity.
[0090] FIG. 2 is a graph concerning the conductive carbon in
Comparative Example 2 and Example 1 that shows the result of an
ultramicro hardness test in which a pressing depth was increased to
the order of nm and a corresponding pressing load was measured. The
ultramicro hardness test was conducted by using the following
method. 10 mg of the conductive carbon in Comparative Example 2 or
Example 1 was dispersed in 50 mg ethanol, and the dispersoid
obtained was coated on a glass plate and dried. By observing the
surface of the glass plate through a microscope, a substantially
spherical aggregate with a diameter of approximately 50 .mu.m was
selected, and the ultramicro hardness test was conducted on the
selected aggregate. In the test, a hardness testing device with a
spherical indenter with a radius of 100 .mu.m (TI 950
Tribolndenter, manufacturer: Hysitron, Inc.) was employed and the
change in the corresponding pressing load was measured while the
pressing depth was increased in increments of 0.07 .mu.m. As can be
seen in FIG. 2, it was found that in the case of the conductive
carbon in Comparative Example 2, the pressing load drastically
increased in the vicinity of the pressing depth of approximately 10
.mu.m, and the aggregated carbon particles were hard to transform.
On the other hand, in the case of the conductive carbon in Example
1, the pressing load gradually increased and several fluctuations
in loading occurred within the range of 0 to 20 .mu.m of pressing
depth. It is conceivable that the fluctuation in loading that can
be seen at approximately 4 to 9 .mu.m of pressing depth corresponds
to the change in loading because a vulnerable area of the aggregate
was severed, and a gradual increase in loading in the range of
approximately 9 .mu.m or more of pressing depth corresponds to the
flexible transformation of the entire aggregate. This flexible
transformation is a significant characteristic of the conductive
carbon of the present invention. That is, in the slurry containing
the gross particles of LiFePO.sub.4, the fine particles of
LiFePO.sub.4 and the conductive carbon of the present invention,
this conductive carbon covers the surface of the gross particles
and the fine particles. After this slurry is applied to the
aluminum foil and dried, the rolling treatment is given to the
slurry, so that the conductive carbon, while being transformed in
accordance with the added pressure, is pushed out between the
adjacent gross particles together with the fine particles. It is
considered that the electrode density is significantly increased
accordingly.
[0091] Since the treatment of the strong oxidizing process involves
a change in the surface functional group of the carbon, this change
in the surface functional group can be confirmed by analyzing a
hydrophilic component of conductive carbon, so the ultraviolet
visible spectrum of the remaining portion of the hydrophilic
component (the liquid phase of the superintendent), from which the
hydrophilic solid phase component had been taken, was measured.
FIG. 3 shows the ultraviolet visible spectra of the abovementioned
liquid phases of the conductive carbon in Comparative Example 2 and
Example 1. In the spectrum of Example 1, the .pi.-.pi.* transition
in a small fraction (a small-size graphene) that was not found in
the spectrum of Comparative Example 2 was clearly recognized, and
it was found that the graphene was severed into small-sized
fragments in the strong oxidizing process.
[0092] FIG. 4 shows the Raman spectra in the range from 980 to 1780
cm.sup.-1 of the hydrophilic solid phase components of conductive
carbon in Comparative Example 2 and Example 1 and the results of
waveform separation. It was found that, in the spectrum of Example
1, compared with the spectrum of Comparative Example 2, the peak
area of the component d, which derives from ideal graphite, was
decreased, while the peak area of the component c, which derives
from the amorphous component, and the peak area of the component e,
which derives from the graphite with an oxidized surface, were
increased. This shows that in the course of the strong oxidizing
process, the conjugated double bond (SP.sup.2 hybridization) of the
graphene in the carbon raw material is strongly oxidized and that a
large amount of the carbon single bond (SP.sup.3 hybridization)
area, that is, the amorphous component, is formed.
[0093] FIG. 5 shows the SEM images taken after the conductive
carbon of Example 1, the conductive carbon of Comparative Example 2
or the hydrophilic solid phase component of the conductive carbon
of Example 1 were each dispersed in a dispersion medium, the
dispersoid obtained was coated on an aluminum foil, and a dried
coating film was obtained. The SEM images taken after a rolling
treatment at 300 kN was given to the coating films are also shown.
The coating film of the conductive carbon of Comparative Example 2
did not show a significant change before and after the rolling
treatment. However, in the case of the coating film of the
conductive carbon of Example 1, as can be seen in the SEM images,
the asperity of the surface was remarkably decreased by the rolling
treatment and the carbon spread in a paste-like manner. Therefore,
it was found that the characteristics of the carbon significantly
changed due to the strong oxidizing treatment. Comparison of the
SEM images of the coating film of the hydrophilic solid phase
component of the conductive carbon of Example 1 and the SEM images
of the coating film of the conductive carbon of Example 1 reveals
that the surface of the coating film of the hydrophilic solid phase
component became flatter by the rolling treatment and the carbon
further spread in a paste-like manner. Based on this result, it was
considered that the characteristic of the conductive carbon of
Example 1 of spreading in a paste-like manner was mainly
attributable to the hydrophilic solid phase component.
[0094] FIG. 6 shows the relationship between the amorphous
component ratio of the hydrophilic solid phase component in the
conductive carbon and the electrode density in Examples 1 to 3 and
Comparative Examples 1 and 2. As this graph suggests, if the
amorphous component ratio increases, the electrode density
increases remarkably, but if the amorphous component ratio becomes
13% or more, the increase ratio of the electrode density tends to
be saturated. Based on this result, it was found that an electrode
of a lithium ion secondary battery with high electrode density
could be obtained stably and reproducibly by making the amorphous
component ratio 13% or more.
(2) The Influence of Structure
Comparative Example 3
[0095] As mentioned above, a carbon structure is severed in the
strong oxidizing process. To investigate the effect of a reduction
in the size of structure, commercially available conductive carbon
(DBP oil absorption quality=134.3 mL/100 g), which has almost the
same DBP oil absorption quality as the conductive carbon of Example
1 (DBP oil absorption quality=130 mL/100 g) but for which the
amorphous component ratio of the hydrophilic solid phase component
is smaller than the range of the present invention, was used
instead of the conductive carbon of Example 1, a positive electrode
containing LiFePO.sub.4 that was obtained by same method as in
Example 1 was manufactured, and the electrode density was
calculated. The electrode density obtained was 2.4 g/cm.sup.3. This
result revealed that reduction in the structure alone did not
achieve improvement in electrode density.
(3) The Influence of Carbon Raw Material
Comparative Example 4
[0096] Instead of Ketjen Black, which was used as a carbon raw
material in Example 1, solid acetylene black (diameter of initial
particle: 40 nm) was used, and the procedure of Example 1 was
repeated. As a result, the amorphous component ratio of the
hydrophilic solid phase component was not increased by the strong
oxidizing treatment to within the range of the present invention,
the electrode density was 2.35 g/cm.sup.3 and improvement in the
electrode density was not achieved. Therefore, it was found that
usage of a carbon material with an inner vacancy as a raw material
was important.
(4) Conductive Carbon Obtained by the Second Manufacturing
Method
Example 4
[0097] Ketjen Black (EC300J, manufacturer: Ketjen Black
International Co.) weighing 0.45 g was mixed with 4.98 g
Co(CH.sub.3COO).sub.2.4H.sub.2O, 1.6 g LiOH.H.sub.2O and 120 mL
distilled water, and the mixed fluid obtained was agitated by a
stirrer for 1 hour, and then a mixture was collected by filtering.
Then, 1.5 g LiOH.H.sub.2O was mixed through an evaporator and then
heated at 250.degree. C. for 30 minutes in air, and a complex in
which a lithium cobalt chemical compound was supported by Ketjen
Black was obtained. 1 g of the complex obtained was added to 100 mL
aqueous solution in which concentrated sulfuric acid (98%),
concentrated nitric acid (70%) and hydrochloric acid (30%) were
mixed at the volume ratio of 1:1:1, and the lithium cobalt chemical
compound in the complex was dissolved by irradiating the mixed
fluid obtained with an ultrasonic wave for 15 minutes, and then the
residual solid matter was filtered, washed with water and dried. A
part of the solid matter after drying was heated to 900.degree. C.
in air and its weight loss was measured by TG analysis. Until it
was confirmed that the weight loss was 100%, that is, no lithium
cobalt chemical compound remained, the abovementioned process of
dissolving the lithium cobalt chemical compound in the
abovementioned acid aqueous solution, filtering, washing with water
and drying was repeated, so that conductive carbon that did not
contain any lithium cobalt chemical compound was obtained.
[0098] Then, the DBP oil absorption quantity and micropore
distribution of Ketjen Black used and the conductive carbon
obtained were measured. Further, 40 mg of the conductive carbon
obtained was added to 40 mL pure water and the carbon was dispersed
in the pure water by applying ultrasonic irradiation for 30
minutes. The resultant supernatant solution was collected and
centrifuged, a solid phase area was gathered and dried, and a
hydrophilic solid phase component was obtained. For the hydrophilic
solid phase component obtained, a Raman spectrum was measured with
a microscopic Raman measurement device (excitation ray: argon ion
laser; wavelength: 514.5 nm). From the Raman spectrum obtained, the
amorphous component ratio, La, Leq, and Leq/La were calculated. The
conductive carbon obtained showed almost the same DBP oil
absorption quantity, reduction rate in the number of pores with the
radius of 1.2 nm, and amorphous component ratio, and values of La,
Leq, and Leq/La as the conductive carbon in Example 1.
(5) Evaluation as a Lithium Ion Secondary Battery
Example 5
[0099] Li.sub.2CO.sub.3, Co(CH.sub.3COO).sub.2 and
C.sub.6H.sub.8O.sub.7.H.sub.2O were introduced into distilled
water, the mixed fluid obtained was agitated by a stirrer for 1
hour, and then the mixed fluid was evaporated, dried and solidified
at 100.degree. C. in air and was then heated at 800.degree. C. in
air for 10 minutes, and LiCoO.sub.2 fine particles with an average
diameter of 0.5 .mu.m were obtained. These particles, commercially
available LiCoO.sub.2 gross particles (average diameter: 13 .mu.m)
and the conductive carbon obtained in Example 1 were mixed at the
mass ratio of 9:90:1, and an electrode material was obtained. Then,
5% by mass of the total mass of polyvinylidene fluoride and an
adequate quantity of N-methyl pyrrolidone were added to the
electrode material and kneaded sufficiently so that slurry was
formed, and this slurry was coated on an aluminum foil, and an
active material layer was formed. The active material layer was
dried and then given a rolling treatment, and a positive electrode
for a lithium ion secondary battery was obtained. The electrode
density of the positive electrode was calculated from the measured
values of the volume and weight of the active material layer on the
aluminum foil in the positive electrode. Also, using the positive
electrode obtained, a lithium ion secondary battery was
manufactured in which a 1M LiPF.sub.6 solution with 1:1 ethylene
carbonate/diethyl carbonat was used as an electrolytic solution,
and in which lithium was used as a counter electrode. The capacity
density per volume of the battery obtained was measured at the rate
of 0.1 C.
Example 6
[0100] Fine particles with an average diameter of 2 .mu.m were
obtained by changing the duration of heating at 800.degree. C. in
air in the manufacturing process of LiCoO.sub.2 particles in
Example 5. The procedure of Example 5 was repeated by using the
fine particles obtained, which had an average diameter of 2 .mu.m,
instead of the fine particles with an average diameter of 0.5
.mu.m.
Example 7
[0101] Fine particles with an average diameter of 2.5 .mu.m were
obtained by changing the duration of heating at 800.degree. C. in
air in the manufacturing process of LiCoO.sub.2 particles in
Example 5. The procedure of Example 5 was repeated by using the
fine particles obtained, which had an average diameter of 2.5
.mu.m, instead of the fine particles with an average diameter of
0.5 .mu.m.
Comparative Example 5
[0102] Commercially available LiCoO.sub.2 gross particles (average
diameter: 13 .mu.m) and acetylene black, which was used as a carbon
raw material in Comparative Example 4, were mixed at the mass ratio
of 99:1, and an electrode material was obtained. Then, 5% by mass
of the total mass of polyvinylidene fluoride and an adequate
quantity of N-methyl pyrrolidone were added to the electrode
material and kneaded sufficiently so that slurry was formed, and
this slurry was coated on an aluminum foil, and an active material
layer was formed. The active material layer was dried and then
given a rolling treatment, and a positive electrode for a lithium
ion secondary battery was obtained. The electrode density of the
positive electrode was calculated from the measured values of the
volume and weight of the active material layer on the aluminum foil
in the positive electrode. Also, using the positive electrode
obtained, the capacity density per volume was measured by the same
process as the process in Example 5.
Example 8
[0103] Li.sub.2CO.sub.3, Ni(CH.sub.3COO).sub.2,
Mn(CH.sub.3COO).sub.2 and Co(CH.sub.3COO).sub.2 were introduced
into distilled water, the mixed fluid obtained was agitated by a
stirrer for 1 hour, and then the mixed fluid was evaporated, dried
and solidified at 100.degree. C. in air. The solidified material
was blended with a ball mill, and then heated at 800.degree. C. in
air for 10 minutes, and LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2
fine particles with an average diameter of 0.5 .mu.m were obtained.
These particles, commercially available
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 gross particles (average
diameter: 7.5 .mu.m) and the conductive carbon obtained in Example
1 were mixed at the mass ratio of 8:90:2, and an electrode material
was obtained. Then, 5% by mass of the total mass of polyvinylidene
fluoride and an adequate quantity of N-methyl pyrrolidone were
added to the electrode material and kneaded sufficiently so that
slurry was formed, and this slurry was coated on an aluminum foil,
and an active material layer was formed. The active material layer
was dried and then given a rolling treatment, and a positive
electrode for a lithium ion secondary battery was obtained. The
electrode density of the positive electrode was calculated from the
measured values of the volume and weight of the active material
layer on the aluminum foil in the positive electrode. Also, using
the positive electrode obtained, a lithium ion secondary battery
was manufactured in which a 1M LiPF.sub.6 solution with 1:1
ethylene carbonate/diethyl carbonate was used as an electrolytic
solution, and in which lithium was used as a counter electrode. The
capacity density per volume of the battery obtained was measured at
the rate of 0.1 C.
Example 9
[0104] Fine particles with an average diameter of 2 .mu.m were
obtained by changing the duration of heating at 800.degree. C. in
air in the manufacturing process of a
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 particle in Example 8. The
procedure of Example 8 was repeated by using the fine particles
obtained, which had an average diameter of 2 .mu.m, instead of the
fine particles with an average diameter of 0.5 .mu.m.
Example 10
[0105] Fine particles with an average diameter of 2.5 .mu.m were
obtained by changing the duration of heating at 800.degree. C. in
air in the manufacturing process of a
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 particle in Example 8. The
procedure of Example 8 was repeated by using the fine particles
obtained, which had an average diameter of 2.5 .mu.m, instead of
the fine particles with an average diameter of 0.5 .mu.m.
Comparative Example 6
[0106] Commercially available
LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 gross particles (average
diameter: 7.5 .mu.m) and acetylene black, which was used as a
carbon raw material in Comparative Example 4, were mixed at the
mass ratio of 98:2, and an electrode material was obtained. Then,
5% by mass of the total mass of polyvinylidene fluoride and an
adequate quantity of N-methyl pyrrolidone were added to the
electrode material and kneaded sufficiently so that slurry was
formed, and this slurry was coated on an aluminum foil, and an
active material layer was formed. The active material layer was
dried and then given a rolling treatment, and a positive electrode
for a lithium ion secondary battery was obtained. The electrode
density of the positive electrode was calculated from the measured
values of the volume and weight of the active material layer on the
aluminum foil in the positive electrode. Also, using the positive
electrode obtained, the capacity density per volume was measured by
the same process as the process in Example 8.
[0107] Table 2 shows electrode density and capacity density per
volume in Examples 5 to 10 and Comparative Examples 5 and 6.
TABLE-US-00003 TABLE 2 Electrode density and capacity density Fine
particle Gross particle Particle Particle Carbon Electrode Capacity
Active diameter Compounding Active diameter Compounding Compounding
density density material (.mu.m) ratio material (.mu.m) ratio Type
ratio (g/cc) (mA/cc) Example 5 LCO 0.5 9 LCO 13 90 Example 1 1 4.2
600 Example 6 LCO 2.0 9 LCO 13 90 Example 1 1 4.0 571 Example 7 LCO
2.5 9 LCO 13 90 Example 1 1 3.9 557 Comparative -- -- -- LCO 13 99
AB 1 3.7 476 Example 5 Example 8 NCM 0.5 8 NCM 7.5 90 Example 1 2
4.1 656 Example 9 NCM 2.0 8 NCM 7.5 90 Example 1 2 3.5 560 Example
10 NCM 2.5 8 NCM 7.5 90 Example 1 2 3.4 544 Comparative -- -- --
NCM 7.5 98 AB 2 3.4 490 Example 6 LCO: LiCoO.sub.2 NCM:
LiN.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 AB: acetylene black
[0108] Comparing the electrode materials of Examples 5 to 7 with
the electrode material of Comparative Example 5, the quantity of
active material contained in the electrode materials is the same,
but in the electrode materials of Examples 5 to 7, some of the
active material particles are fine particles. Similarly, comparing
the electrode materials of Examples 8 to 10 with the electrode
material of Comparative Example 6, the quantity of an active
material contained is the same, but in the electrode materials of
Examples 8 to 10, some of active material particles are fine
particles. Fine particles are generally prone to aggregation, but
as can be seen from Table 2, the electrode density and capacity
density were increased by using the conductive carbon in Example 1.
Especially, the increase in capacity density was remarkable.
Moreover, in Examples, the electrode density and capacity density
were increased more as the particle diameter of the fine particles
was decreased. From these results and the result shown in FIG. 5,
it was found that the conductive carbon of the present invention
dispersed fine particles as well as gross particles excellently,
and by applying a rolling treatment in manufacturing an electrode,
the conductive carbon of the present invention spread in a
paste-like manner, covered the surface of the active material
particles, and together with the fine particles, was pushed out
into and densely filled a gap formed between adjacent gross
particles. Also, from the remarkable increase in the capacity
density, it was found that the dense, paste-like conductive carbon
that was formed by adding pressure to the conductive carbon of the
present invention had enough conductivity to serve as an
electroconductive agent and did not inhibit the impregnation of the
electrolytic solution in the lithium ion secondary battery.
(6) The Influence of an Average Diameter of Fine Particles
Example 11
[0109] Li.sub.2CO.sub.3, Co(CH.sub.3COO).sub.2 and
C.sub.6H.sub.8O.sub.7.H.sub.2O were introduced into distilled
water, the mixed fluid obtained was agitated by a stirrer for 1
hour, and then the mixed fluid was evaporated, dried and solidified
at 100.degree. C. in air and then heated at 800.degree. C. in air,
and LiCoO.sub.2 fine particles were obtained. In this process, by
changing the duration of heating at 800.degree. C. in air, more
than one kind of fine particles with a different average diameter
was obtained. One of these kinds of fine particles with a different
average diameter, commercially available LiCoO.sub.2 gross
particles (average diameter: 13 .mu.m), the conductive carbon
obtained in Example 1, and the acetylene black used as a carbon raw
material in Comparative Example 4 were mixed at the mass ratio of
9:90:1:2, and an electrode material was obtained. Then, 5% by mass
of the total mass of polyvinylidene fluoride and an adequate
quantity of N-methyl pyrrolidone were added to the electrode
material and kneaded sufficiently so that slurry was formed, and
this slurry was coated on an aluminum foil, and an active material
layer was formed. The active material layer was dried and given a
rolling treatment, and a positive electrode of a lithium ion
secondary battery was obtained. The electrode density of the
positive electrode was calculated from the measured values of the
volume and weight of the active material layer on the aluminum foil
in the positive electrode.
[0110] FIG. 7 shows the relationship between the average diameter
of the fine particles obtained and the electrode density. It was
found that the electrode density rapidly increased if the average
diameter of the fine particles became 2 .mu.m or less. As electrode
density increases, the capacity density and accordingly the energy
density of a battery increases, so it was found that a lithium ion
secondary battery with high energy density can be obtained by using
the gross particles with an average diameter of 15 .mu.m and the
fine particles with an average diameter of 2 .mu.m or less.
Example 12
[0111] Li.sub.2CO.sub.3, Ni(CH.sub.3COO).sub.2,
Mn(CH.sub.3COO).sub.2 and Co(CH.sub.3COO).sub.2 were introduced
into distilled water, the mixed fluid obtained was agitated by a
stirrer for 1 hour, and then the mixed fluid was evaporated, dried
and solidified at 100.degree. C. in air. The solidified material
was blended in a ball mill, and then heated at 800.degree. C. in
air, and LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 fine particles
were obtained. In this process, by changing the duration of heating
at 800.degree. C. in air, more than one kind of fine particles with
a different average diameter was obtained. One of these kinds of
fine particles with a different average diameter, commercially
available LiNi.sub.0.5Mn.sub.0.3Co.sub.0.2O.sub.2 gross particles
(average diameter: 7.5 .mu.m), the conductive carbon obtained in
Example 1, and the acetylene black used as a carbon raw material in
Comparative Example 4 were mixed at the mass ratio of 8:90:2:2, and
an electrode material was obtained. Then, 5% by mass of the total
mass of polyvinylidene fluoride and an adequate quantity of
N-methyl pyrrolidone were added to the electrode material and
kneaded sufficiently so that slurry was formed, and this slurry was
coated on an aluminum foil, and an active material layer was
formed. The active material layer was dried and given a rolling
treatment, and a positive electrode of a lithium ion secondary
battery was obtained. The electrode density of the positive
electrode was calculated from the measured values of the volume and
weight of the active material layer on the aluminum foil in the
positive electrode.
[0112] FIG. 8 shows the relationship between the average diameter
of the fine particles obtained and the electrode density. It was
found that the electrode density rapidly increased if the average
diameter of the fine particles became 2 .mu.m or less. As electrode
density increases, the capacity density and accordingly the energy
density of a battery increases, so it was found that a lithium ion
secondary battery with high energy density can be obtained by using
the gross particles with an average diameter of 7.5 .mu.m and the
fine particles with an average diameter of 2 .mu.m or less.
INDUSTRIAL APPLICABILITY
[0113] By using the conductive carbon of the present invention, an
electric storage device with a high energy density can be
obtained.
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